Mark IIB to IIC+ Conversion

[Jay Omega]

Boogie quit upgrading IIBs to IIC+s some time ago, so having them turn my IIB HRG into a IIC+ is unfortunately not an option. I'm incredibly stubborn, IIC+ prices are higher than I can justify, and I'm pretty set on having a IIC+ so I decided to convert it myself.

Over the past couple years I've struggled with the conversion, which is essentially a new preamp card. I've replaced the card in the amp twice already I think, and tried a separate scratch build. Each time I've ended up with annoying issues, most annoying was a ground loop that I was unable to fix in the last couple attempts.

I'm 50.1% confident I figured out the problem, but I don't have the guts to try another preamp board in the Boogie amp just yet, so I started yet another scratch build which would be similar to a SRG. The hope is that I can get the amp working the way I want (perfectly) and then make another preamp board and finish the IIB -> IIC+ project.

Thought I'd share some pictures of the process, and if I get it finished I'll add some pictures of the IIB conversion in this thread as well.

I think the chassis work is finished, so next step will be making the circuit cards.

 

[Jay Omega]

Got the three single-sided boards etched today

 

[Jay Omega]

Here is the EQ driver card completed

Edit - the Darlington is installed backwards in this picture, I fixed it afterwards

 

[Jay Omega]

Got the power supply card done and drilled the tube socket holes in the power amp card.

I haven’t installed any biasing resistors yet, will determine the values using a potentiometer when I get it all wired up

 

[JD]

Love this great work

 

[woodbutcher65]

Would you be willing to share your files or sell board sets?

 

[Jay Omega]

Would you be willing to share your files or sell board sets?

I can't see myself selling board sets as they're specific to the parts I have, my chassis design, any layout decisions I made, etc, not to mention the cost would be hard to justify. There are IIC+ board sets already available on the market, I even bought a preamp card from a kind fella on sloclone at one point but didn't try it. I spoke with Mike B about what I was trying to do with the IIB, he knew about and recommended "some guy in Europe" that sold IIC+ preamp cards that people were using, that may have been the sloclone seller. Regarding sharing any design files, unsure how I feel about it, there's a lot to ponder there.

I've thought about writing a book about the IIC+ design as I'm pretty familiar with the amps at this point, and maybe would include some guidance for people that want to start dabbling in tube amp electronics.

 

[Jay Omega]

Love this great work

Thank you for the kind words!

 

[Jay Omega]

Got the power amp and graphic PCBs finished and the graphic populated.

Hopefully I’ll populate the power amp card tomorrow and can start wiring the amp.

 

[Jay Omega]

Ready for install

 

[Henz]

Ready for install

View attachment 365

Looks awesome. Very neat and clean!! . I've always wondered what the two 100 ohm resistors do off the heater supply to ground. And dang, I would love to know where I can get those darker red caps (.047 and .0005 uf ?) . Hard to find 600v caps that small. Blessings, Jim.

 

[Jay Omega]

Looks awesome. Very neat and clean!! . I've always wondered what the two 100 ohm resistors do off the heater supply to ground.

Their purpose is to reduce hum. The resistors create a virtual center tap for the heater winding and reference the circuit to ground. Check out The Valve Wizard Heater / Filament supplies on the net to learn more

 

[Henz]

Their purpose is to reduce hum. The resistors create a virtual center tap for the heater winding and reference the circuit to ground. Check out The Valve Wizard Heater / Filament supplies on the net to learn more

Ty for the reply! And dang, I would love to know where I can get those darker red caps (.047 and .0005 uf ?) . Hard to find 600v caps that small. Blessings, Jim.

 

[Jay Omega]

Ty for the reply! And dang, I would love to know where I can get those darker red caps (.047 and .0005 uf ?) . Hard to find 600v caps that small. Blessings, Jim.

The dark red are 47 and 100 nF, I believe both are 250V CDE DME series. I probably got them from Mouser

 

[woodbutcher65]

Is that EQ board a drop-in fit for a Mesa chassis? (Ignoring the two toggle switches)

 

[Jay Omega]

Is that EQ board a drop-in fit for a Mesa chassis? (Ignoring the two toggle switches)

It’s pretty close, but no. When I measured the slots on my IIB faceplate, I found that the graphic pots are not equidistant. I laid out everything equidistant for this build, and I have more chassis height so mine is taller as well

 

[Jay Omega]

Wiring has begun, will probably send another update when I’ve got the power supply, graphic and power amp wired and tested

 

[Jay Omega]

Got the power amp wired and tested tonight, don’t mind the sloppy temporary wiring.

Used JJ 6L6GCs for the test, getting 496 V on the plate at 40 mA plate current, leaving the tubes around 20 W at idle. Bias voltage was approx -51 V.

 

[Henz]

Got the power amp wired and tested tonight, don’t mind the sloppy temporary wiring.

View attachment 415

Used JJ 6L6GCs for the test, getting 496 V on the plate at 40 mA plate current, leaving the tubes around 20 W at idle. Bias voltage was approx -51 V.

Fantastic! Those voltages are real close to mine. As mentioned, I'm A DIY learner. That temp pot, is that for bias adjusting. If so, how and why did you do it on a " fixed" bias amp? I see ,I think, that the pot is hooked to the two 47uf, 100v bias caps. What was the purpose? Ty. Blessings, Jim

 

[Jay Omega]

Fantastic! Those voltages are real close to mine. As mentioned, I'm A DIY learner. That temp pot, is that for bias adjusting. If so, how and why did you do it on a " fixed" bias amp? I see ,I think, that the pot is hooked to the two 47uf, 100v bias caps. What was the purpose? Ty. Blessings, Jim

Yes, it was to determine the value of the fixed resistor, I replaced it with a 33k resistor.

What resistor values do you have in yours? There should be two on the edge of the board, they are referred to as factory set on most drawings I’ve seen